<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        table {
            border: 1px solid #000;
            text-align: center;
            width: 240px;
        }

        th,
        td {
            border: 1px solid #000;
        }

        h3 {
            position: relative;
        }
    </style>
</head>

<body>
    <div id="app">
        <h3>小黑的礼物清单</h3>
        <!-- 首先渲染数据 -->
        <table>
            <tr>
                <th>名字</th>
                <th>数量</th>
            </tr>
            <tr v-for="e in list" :key="e.id">
                <td>{{e.name}}</td>
                <td>{{e.num}}个</td>
            </tr>
        </table>

        <!-- 目标：统计求和，求得礼物总数 -->
        <p>礼物总数：{{add}} 个</p>
    </div>
    <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
    <script>
        const app = new Vue({
            el: '#app',
            data: {
                // 现有的数据
                list: [
                    { id: 1, name: '篮球', num: 1 },
                    { id: 2, name: '玩具', num: 2 },
                    { id: 3, name: '铅笔', num: 5 },
                ]
            },
            computed: {//与data同级
                // 复杂写法
                add: {//语法中必须有return
                    get() {
                        return this.list.reduce((prev, e) => prev + e.num, 0)
                    },
                    set(newVal) {//此处为数值改变后使用
                        console.log(newVal)
                    }
                }
            }
        })
    </script>
</body>

</html>